Inverse photochromism in viologen–tetraarylborate ion-pair complexes: optical write/microwave erase switching in polymer matrices

Willy G Santos,Darya S Budkina,Malcolm D E Forbes,Daniel R Cardoso,Alexander N Tarnovsky,Pedro F G M Da Costa

doi:10.1039/d1ma01030a

Willy G Santos, Darya S Budkina + Show 4 more

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https://doi.org/10.1039/d1ma01030a

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Abstract

The spin dynamics of radical pairs from ion-pair complexes between viologen and tetraarylborate compounds have been investigated in the presence of microwave (μw) radiation, using steady-state electron paramagnetic resonance to follow the radical pair dynamics.

Highlights

We focus on electron donor−acceptor systems based on an ion pair complex of a viologen dication and tetraarylborate anion in which photoinduced electron transfer from the tetraarylborate to the viologen produces a radical pair (RP) characterized as the Fully Charge Separated (FCS) state
In contrast with X-ray diffraction observed for compounds 1a:2a and 1b:2a, theDOaIb: 1s0e.10n3cV9iee/wD1oAMrftiAcl0e1O0n3l0inAe a diffraction signal for the 1b:2b and 1b:2a complexes made it impossible to determine the molecular structure of the respective crystals
The excited state transient absorption events and stimulated emission of viologen-borate complexes of all ion pair complexes based on this viologen–tetraarylborate framework have been investigated in detail via excitation of the charge-transfer band around 400–700 nm

Summary

Introduction

Photochromism of viologen type molecule is the reversible transformation of the viologen specie between two forms, non-radical (V2+) and radical (V+). The radical form has different uv-vis absorption spectra from non-radical species that the absorbance is only observed in the ultraviolet region. Stable ion-pair systems, such as viologen-borate based compounds developed in our laboratories over the past several years, can exhibit interesting photoinduced color changes, where the most stable form is pale yellow or orange and acquires coloration when irradiated with blue light (400-450 nm).7 This property often derives from a photocatalyzed electron transfer reaction from the borate anion to the viologen dication. Ion-pair complexes based on viologen structure are of significant interest in this regard, as they can exhibit charge transfer (CT) character in their excited singlet states as one of their decay paths.7 Spin selectivity in such processes can be exploited using electromagnetic radiation as an external trigger, which can lead to precise control of the motion of charge and spin on the molecular and nanometer scales. This photoinduced electron transfer pathway can lead to diverse optical functionality such as photochromism, as previously observed by us.

Background

Results and Discussion

Conclusions